Solid oxide fuel cell device and method for manufacturing same

ABSTRACT

To provide SOFC and method for manufacturing same, capable of preventing breakage of fuel cell electrodes, and of securing an electrical connection between fuel cells and a current collector. SOFC 1 comprising a cell array composed of fuel cells 16, and current collector 82 connected to electrodes formed on fuel cells 16, wherein current collector 82 is a metal plate on which attaching holes 84 are formed; elastic pieces 84a are provided on each attaching hole 84; current collector 82 is attached to the cell array using elastic pieces 84a, by the insertion of fuel cell 16 into attaching holes 84; and elastic pieces 84a are affixed to fuel cells 16 by electrode protective layer 152 so that the positions of elastic pieces 84a are not displaced relative to the electrodes on fuel cells 16.

RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2014-044876 filed on Mar. 7, 2014, 2014-044875 filed on Mar. 7, 2014 and 2014-044878 filed on Mar. 7, 2014, the entire contents of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to a solid oxide fuel cell device and method for manufacturing the same, and in particular to a solid oxide fuel cell device and method for manufacturing the same comprising a current collector electrically connecting a plurality of individual fuel cells housed in a fuel cell module.

2. Description of the Related Art

A solid oxide fuel cell (“SOFC” below) device is a fuel cell device which operates at a relatively high temperature in which, using an oxide ion conducting solid electrolyte as an electrolyte, with electrodes attached to both sides thereof, fuel gas is supplied to one side and oxidizer gas (air, oxygen, or the like) is supplied to the other side.

The solid oxide fuel cell device houses, within a fuel cell module, a cell array formed of a plurality of individual fuel cells (cell tubes). In this cell array, the plurality of individual fuel cells are electrically interconnected by a current collector. For example, in the fuel cell device set forth in Japanese Published Unexamined Patent Application 2008-71711 (Patent Document 1), the top ends and bottom ends of the plurality of individual fuel cells are respectively inserted into holes in electrically insulating support plates and affixed to the support plates using an electrically conductive seal material. Furthermore, connections are made using a connecting member between top end portions and between bottom end portions of adjacent individual fuel cells, mediated by an electrically conductive seal material.

In the fuel cell device set forth in Japanese Published Unexamined Patent Application 2008-218005 (Patent Document 2), the top end portions and bottom end portions of a large number of individual fuel cells are electrically interconnected using 3 current collectors.

3. Prior Art References—Patent Citations

Patent Document 1: Japanese Published Unexamined Patent Application 2008-71711

Patent Document 2: Japanese Published Unexamined Patent Application 2008-218005

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

For a fuel cell device such as that in Patent Document 1, however, the work of electrically interconnecting individual fuel cells becomes extremely cumbersome when connecting between adjacent individual fuel cell end portions at the two end portions of the individual fuel cells using connecting members and seal material if there is a large number of individual fuel cells.

On the other hand, in the fuel cell device of Patent Document 2, a large number of individual fuel cell end portions are electrically connected using only 3 current collectors, facilitating the work of electrically connecting the individual fuel cells. Specifically, attaching holes for attaching a plurality of corresponding individual fuel cells are formed on each current collector, and at each attaching hole, a plurality of elastic pieces extend in a radial direction from the edge portion of the hole toward its center. For this reason, the end portions of corresponding individual fuel cells can be pushed into the plurality of attaching holes at each current collector by pressing each current collector relative to a cell array comprising a plurality of individual fuel cells. The plurality of elastic pieces at each attaching hole can then be elastically brought into contact with the outer periphery surface of the corresponding individual fuel cell. Ease of work is thus greatly improved for the work of attaching current collectors to the large number of individual fuel cells, and the work of electrically interconnecting individual fuel cells is simplified.

However, the present inventors discovered the following problems with current collectors such as those set forth in Patent Document 2. Namely, because individual fuel cells are formed of ceramic material, there is variability in the shapes (diameter, length, bend, etc.) of each of the individual fuel cells. Therefore in a cell array formed of a plurality of individual fuel cells, the end portion of each fuel cell is offset from the ideal position.

Hence even if current collectors are positioned relative to a cell array, the axial centers of some of the individual cells are offset relative to corresponding attaching holes of the current collectors, so that in the operation of attaching a current collector to a cell array, the pressing force required to press a current collector onto a cell array is increased. There is also a risk that excessively pushing a current collector onto a cell array may cause an electrode disposed on the outside surface of an individual fuel cell to be peeled off by the elastic piece. Such damage to an electrode adversely affects cell performance and device lifespan.

To facilitate insertion of current collectors into a plurality of individual fuel cells and also prevent peeling of electrodes at the time of insertion, the current collector should be thin to decrease the elasticity of the elastic pieces. However, in the fuel cell device of Citation 2, the current collector and individual fuel cell are brought into contact using the elasticity of the elastic pieces, therefore the electrical connection between the current collector and the individual fuel cell is lost when the elasticity of the elastic pieces declines. In other words, if the current collector thickness is reduced and the elasticity of the elastic piece is decreased, there is a risk that uneven contact by elastic pieces (i.e., failure to appropriately contact the individual fuel cell by a portion of the plurality of elastic pieces of the attaching hole) will occur when attaching the current collector to a cell array, or during operation of the fuel cell device. In particular, if an elastic piece is exposed to a high temperature (e.g., 600° C. or above) during operation, there is a risk that the coefficient of elasticity of the elastic piece will decrease, and the elastic force of the elastic piece will be lost due to recrystallization or the like, thereby causing uneven contact of the elastic piece. When a conductivity failure occurs in some of the elastic pieces, current concentrates in the contacting elastic pieces, thereby concentrating current in certain individual fuel cells or a portion thereof, degrading the specified cell functionality and shortening product lifespan.

Thus in the current collector structure of the fuel cell device of Patent Document 2, the work of attaching the current collector to the cell array was eased, but there was risk of damage to electrodes of individual fuel cells when attaching the current collector, and of poor conductivity occurring between the current collector and individual fuel cells, at least during operation of the fuel cell device.

Therefore in a solid oxide fuel cell device having a structure electrically connecting a plurality of individual fuel cells using a current collector and method for manufacturing the same, the present invention has the object of providing a solid oxide fuel cell device and method for manufacturing the same capable of preventing breakage of electrodes of the individual fuel cells, and of securing an electrical connection between individual fuel cells and the current collector.

Means for Solving Problems

In order to solve the above-described problems, the present invention is a solid oxide fuel cell device comprising a cell array including a plurality of individual fuel cells housed in a fuel cell module, and a current collector electrically connected to electrodes formed on the end portions of the plurality of individual fuel cells constituting the cell array, wherein the current collector is a metal plate in which a plurality of attaching holes are formed for respectively inserting the end portions of the plurality of individual fuel cells, and a plurality of elastic pieces are provided at each attaching hole, the end portions of the individual fuel cells are inserted into the corresponding attaching holes of the current collector, such that the current collector is attached to the cell array by the elastic pieces; and the elastic pieces are adhered to the individual fuel cells by adhesive so that the position of the elastic pieces is not displaced relative to the electrodes of the individual fuel cells.

When elastically attaching a current collector to a cell array by pushing the current collector onto the cell array and causing individual fuel cells to be inserted into a plurality of attaching holes of the current collector, the current collector must be inserted with a large pushing force onto the cell array when elastically attaching the current collector to the cell array, due to the fact that the manufactured dimensional accuracy of individual fuel cells is not high. However, there is a risk that pressing on a current collector with excessive force may damage individual fuel cells (especially the electrode layer). In particular, if the elastic force of an elastic piece formed at the attaching hole of the current collector is large, the electrode layer of individual fuel cells is scratched due to scraping of the outer periphery surface of the individual fuel cells by elastic pieces during insertion.

To avoid such damage to individual fuel cells, the elastic force of the elastic piece must be set low by forming the elastic piece of a thin sheet material. However, if the elastic force of the elastic piece is low, the elastic piece may make uneven contact at time of attachment due to manufacturing dimensional error in individual fuel cells, posing the risk of poor conductivity between elastic pieces and electrodes, starting in manufacturing. Also, if the elastic force of the elastic piece is low, when the current collector is exposed to high temperature during operation of the fuel cell device, the risk will occur such that elastic pieces make uneven contact due to a drop in the elastic force of the elastic pieces and then partial poor conductivity occurs between elastic pieces and electrodes of individual fuel cells.

Therefore in the present invention the current collector is elastically engaged with the cell array using elastic pieces formed at attaching holes formed on the current collector, and elastic pieces are affixed to individual fuel cells by adhesive so that these elastic pieces are not displaced relative to the electrodes of the individual fuel cells (i.e., so that the elastic pieces do not move away from the electrodes). In the invention thus constituted, the elastic pieces are affixed by adhesive so as not to be displaced relative to electrodes, even if the elastic force of the elastic pieces is set low so as not to damage electrodes of individual fuel cells when attaching a current collector to a cell array, therefore during operation of the fuel cell device, electrical conductivity can be secured between the elastic pieces and electrodes even if the elastic force of the elastic pieces is reduced or lost. That is, in the present invention the adhesive force of the adhesive compensates for the amount of reduction in the elastic force of elastic pieces during operation, so conductivity is secured between elastic pieces and the electrodes even if elastic pieces lose their elastic force.

In the present invention, the elastic pieces preferably elastically engage the electrodes of the individual fuel cells by bending in along the side surface of the individual fuel cells, and the adhesive is disposed to cover at least a portion of the bending elastic pieces.

If adhesive viscosity is high, workability is degraded, and it is difficult to apply adhesive over the entire periphery of the individual fuel cell. According to the present invention, however, adhesive is disposed so that at least a portion of the elastic piece bent along the side surface of the individual fuel cells is covered, therefore the elastic piece prevents dripping of adhesive, making it possible to use a low viscosity adhesive.

In the present invention, the adhesive is preferably electrically conductive and is disposed between the elastic pieces and the electrodes of the individual fuel cells, and the adhesive is hardened in a state where at least a portion of the elastic pieces is sunk into the adhesive.

In the invention thus constituted, when a current collector is attached to a cell array and the adhesive hardened, that adhesive hardening is done in a state wherein at least a portion of the elastic piece is sunk into the conductive adhesive, thus increasing the contact surface area between the elastic pieces and the adhesive. Thus contact resistance between the elastic pieces and the adhesive can be reduced, and the electrical and physical adhesion between the elastic pieces and the adhesive can be made stronger.

In the present invention, an electrically conductive electrode protective layer is preferably disposed between the elastic pieces and the electrodes of the individual fuel cells to prevent damage to the electrodes by contact with the elastic pieces when the end portions of the individual fuel cells are inserted into the corresponding attaching holes of the current collector, and the electrode protective layer is the adhesive.

In the invention thus constituted, an electrically conductive electrode protective layer for preventing damage by elastic pieces is formed on the electrode of the individual fuel cell. This enables the prevention of electrode damage caused by the scraping of fuel cell electrodes when inserting individual fuel cells into the current collector. Thus in the present invention electrode damage can be prevented while using a current collector with elastic pieces having a high elastic force. Therefore the present invention enables the suppression of uneven contact by elastic pieces when attaching the current collector, and uneven contact by elastic pieces caused by a drop in elastic force during high temperature operation, and enables good conductivity to be secured between the current collector and individual fuel cells through an electrode protective layer, while maintaining good workability in the attachment of the current collector.

To resolve the aforementioned problems, the present invention is a method for manufacturing a solid oxide fuel cell device comprising a cell array including a plurality of individual fuel cells housed in a fuel cell module, and a current collector electrically connected to electrodes formed on the end portions of the plurality of individual fuel cells constituting the cell array, comprising: an attaching step for attaching the current collector to the cell array, wherein the current collector is a metal plate in which a plurality of attaching holes are formed for respectively inserting the end portions of the plurality of individual fuel cells, a plurality of elastic pieces are provided at each attaching hole, and by pressing the current collector into the cell array, the end portions of the individual fuel cells are inserted into the corresponding attaching holes of the current collector, and the current collector is attached to the cell array by the elastic force of the elastic pieces; and an adhesion step for adhering the elastic pieces of the current collector to the individual fuel cells with adhesive to prevent displacement of the position of elastic pieces relative to the electrodes of the individual fuel cells.

As described above, when a current collector with attaching holes is pressed onto a cell array and the current collector is elastically attached to the cell array using elastic pieces, there is a risk that the electrodes of the individual fuel cells will be damaged by the elastic pieces. However, if the elastic force of the elastic pieces is set at a low level to avoid damaging electrodes, there is a risk of uneven contact at the time of attachment, preventing good electrical contact, or of degraded electrical contact between elastic pieces and electrodes caused by a drop in elastic force in a high temperature operating state.

The present invention is therefore constituted to adhere elastic pieces to individual fuel cells with adhesive after the current collector is attached to the cell array, so the positions of elastic pieces are not displaced relative to the electrodes of the individual fuel cells. In the invention thus constituted, elastic pieces are not displaced relative to electrodes by affixing with adhesive, even if the elastic force of elastic pieces is set to a low level to avoid damage to electrodes of individual fuel cells when the current collector is attached to the cell array. Therefore electrical non-contact caused by a drop in the elastic force of elastic pieces during operation of a solid oxide fuel cell device can be prevented, and a good electrically conductive state assured between elastic pieces and electrodes.

The present invention preferably further comprises an application step for applying electrically conductive adhesive onto the electrodes formed on the end portion of each individual fuel cell in the cell array; wherein in the attaching step, the current collector is attached to the cell array by the elastic force of the elastic pieces, with the elastic pieces contacting the adhesive; and in the adhesion step, the adhesive is hardened to prevent the position of the elastic pieces from being displaced relative to the electrode of the individual fuel cell.

As described above, if a current collector with attaching holes is pushed onto a cell array and the current collector is elastically attached to the cell array using elastic pieces, there is a risk that a portion of the elastic pieces will not make physical contact with the electrodes of the individual fuel cell because dimensional accuracy in manufacturing individual fuel cells is low. That is, there is a risk of uneven contact. To prevent uneven contact, elastic piece elastic force should be set high. However when elastic piece elastic force is large, there is a risk of individual fuel cell electrodes being damaged by elastic pieces when attaching a current collector to a cell array. Therefore there is a limit on the degree of elastic force which can be set for the elastic piece.

With this in mind, in the present invention an electrically conductive paste-form adhesive is first applied onto individual fuel cells in the cell array. When doing so, it is preferable to adjust adhesive viscosity and apply the adhesive thickly on the electrode surfaces. Next, the current collector is attached to the cell array. If the current collector has been attached to the cell array, there is a risk that even though some of the elastic pieces physically contact an electrode, remaining elastic pieces do not physically contact an electrode due to variability in manufacturing dimensions. With the present invention, however, all the elastic pieces can at least be brought into contact with a layer of paste-form adhesive having some thickness. Elastic pieces can preferably be sunk into a layer of adhesive. Therefore elastic pieces can be made to contact adhesive even if the elastic pieces are not directly contacting an electrode. By hardening adhesive in this state, elastic pieces can be affixed to electrodes via the hardened adhesive so that the elastic pieces are not displaced relative to electrodes. Since the adhesive is electrically conductive, the physical connection between elastic pieces and electrodes through adhesive enables a state of electrical connection between elastic pieces and electrodes to be secured.

Thus in the present invention elastic pieces not contacting electrodes and electrodes can be physically joined, and thereby electrically connected, via the electrically conductive adhesive. Therefore in the present invention even if elastic piece elastic force is set low, electrical contact between the current collector and the cell array can be secured without increasing the dimensional accuracy of individual fuel cells, and the occurrence of poor electrically conductivity between elastic pieces and electrodes associated with a drop in elastic force during high temperature operation can be avoided.

The present invention preferably further comprises: an application step for applying electrically conductive adhesive onto the electrodes formed on the end portions of the plurality of individual fuel cells; a first hardening step for implementing a first hardening of adhesive applied onto the plurality of individual fuel cells so as to enable assembly of the plurality of individual fuel cells into the cell array; and a modularization step for forming the cell array of the plurality of individual fuel cells; wherein in the attaching step, the current collector is attached to the cell array by the elastic force of the elastic pieces with the elastic pieces elastically brought into contact with the first hardened adhesive; and the adhesion step includes a second hardening step for heating the first hardened adhesive to cause a second hardening, wherein in the second hardening step, as the second hardening is proceeding, portions of the elastic pieces are caused to sink into the adhesive by the elastic force of the elastic pieces, and the adhesive is caused to fully harden with the portions of elastic pieces sunk into the adhesive such that the elastic pieces and the electrode are adhered through the adhesive and the position of the elastic pieces is prevented from being displaced relative to the electrodes of the individual fuel cells.

In the invention thus constituted, adhesive is applied to electrodes of individual fuel cells with the individual fuel cells in a standalone state, and the adhesive is hardened to a degree allowing for subsequent assembly work to be performed (first hardening). Thereafter, the plurality of individual fuel cells are modularized into a cell array. If, unlike this invention, adhesive is applied onto the individual fuel cells after modularization, reliable application assuring electrical conductivity will be difficult and extremely cumbersome, since the plurality of individual fuel cells are disposed in dense proximity. However, in the present invention adhesive is applied onto the individual fuel cells in a standalone state, therefore good workability is achieved.

Also, in the present invention a further complete hardening of the adhesive (second hardening) is carried out after the current collector is attached to the cell array. This second hardening allows for elastic pieces to be adhered to the adhesive layer hardened in the first hardening. In other words, elastic pieces are made to elastically contact the adhesive layer, therefore during the second hardening a portion of the elastic pieces can be made to sink into the adhesive layer by elastic force, and the second adhesive hardening can be completed with a portion of the elastic pieces sunken into adhesive. The sinking of a portion of the elastic pieces into adhesive increases the contact surface area between the elastic pieces and the adhesive, enabling a stronger affixing of the elastic pieces to the electrode.

The present invention preferably further comprises a step for preparing the cell array made up of the plurality of individual fuel cells, wherein an electrically conductive electrode protective layer is formed on the electrodes formed on the end portions of the individual fuel cells to prevent damage to the electrodes caused by contact with the elastic pieces in the attaching step.

In the invention thus constituted, a current collector having elastic pieces with a large elastic force can be used so that the elastic pieces have sufficient elastic force during attachment and during high temperature operation. Hence in the present invention, when attaching the current collector to the cell array, an electrode protective layer is formed on electrodes to prevent damage to electrodes of individual fuel cells by elastic pieces. This electrode protective layer is an electrically conductive layer harder than the electrode. This electrode protective layer enables individual fuel cells to be protected from peeling of electrodes due to scraping thereof by elastic pieces at the time of attachment. Also, because elastic pieces with a high elastic force elastically engage the electrode protective layer, conduction can be assured between the current collector and electrodes of individual fuel cells through the electrode protective layer.

Thus in the present invention, by adoption of an electrode protective layer, electrodes of individual fuel cells can be protected when attaching a current collector, even if the current collector used has elastic pieces with a large elastic force. As a result, in the present invention damage to electrodes can be prevented while good workability is preserved for attaching the current collector to a cell array. In addition, in the present invention elastic pieces can have a large elastic force, therefore when attaching a current collector and during operation, a state of contact between elastic pieces and electrode protective layers can be held by the elastic force of the elastic piece, thereby preventing uneven contact.

In the present invention the electrode protective layer is preferably the adhesive; and in the adhesion step, the elastic pieces and the electrode protective layer are adhered.

The invention thus constituted comprises an adhesion step for adhering elastic pieces and the electrode protective layer after attaching the current collector to the cell array, therefore a contacting state between the elastic pieces and the electrode protective layer can be secured. As a result, the adhesive force of the adhesive compensates for the amount of reduction in the elastic force of elastic pieces during operation, so conductivity is secured between elastic pieces and the electrode protective layer even if elastic pieces lose their elastic force. Hence it is unnecessary to consider drops in elastic force during operation, so a current collector comprising elastic pieces with an extremely large elastic force is not necessarily required. Therefore in the attaching step, the work of attaching the current collector is eased, and workability is improved.

In the present invention the electrode protective layer preferably has the function of adhering the elastic pieces and the electrodes.

In the invention thus constituted, the electrode protective layer has an adhering function, therefore the operation of applying adhesive is not required after the attaching step, and the manufacturing process can be simplified.

In the present invention the adhering function is preferably activated by heating the electrode protective layer; the method for manufacturing the solid oxide fuel cell device includes a heating step for heating the cell array to perform a certain process, and the heating step doubles as a step for heating the electrode protective layer in the adhesion step.

In the invention thus constituted, the electrode protective layer is constituted so that the adhering function is activated by heating. Therefore while a heating step for the electrode protective layer is necessary, the ability to execute other work on the assembly during the heating step is lost when the heating step is executed on a fuel cell device assembly during manufacturing. Specifically, in the heating step, after heating the assembly to a predetermined temperature, cooling to room temperature is again required, and if rapid cooling is used, a generating element of the individual fuel cell is subjected to stress due to sudden thermal shrinkage. To prevent this type of damage, cooling requires a long duration. Therefore adding a heating step solely for the electrode protective layer during the manufacturing process greatly lengthens the manufacturing process.

The present invention is therefore constituted so that the heating step included in the original manufacturing process (e.g., a reduction step for fuel cells implemented in a final stage) also serves as a heating step for an electrode protective layer. This eliminates the need to add a heating step solely for the electrode protective layer, so that lengthening of the manufacturing process can be prevented and elastic pieces can be adhered to the electrode protective layer.

The present invention preferably comprises a preparation step for preparing the cell array made up of the plurality of individual fuel cells, wherein the electrodes formed on the end portions of the individual fuel cells are porous bodies of a porous electrically conductive material constituting fuel electrodes or air electrodes of the individual fuel cells, and the preparation step further comprises an application step for applying electrically conductive adhesive onto the electrodes of the plurality of individual fuel cells; and in the adhesion step, the elastic pieces and the electrodes of the individual fuel cells are adhered using the adhesive disposed between the elastic pieces and the electrodes of the individual fuel cells.

In the invention thus constituted, the preparation step for the cell array includes an application step for applying electrically conductive adhesive onto the electrodes of the individual fuel cells. After the preparation step, there is the attaching step for attaching the current collector onto the cell array; in this attaching step the current collector is attached to the cell array using the elastic force of the elastic pieces, and adhesive is disposed between the elastic pieces of the current collector and the electrodes of the individual fuel cells. In this attaching step, elastic pieces elastically engage electrodes through an adhesive layer, thereby suppressing electrode breakage so that good workability in attaching the current collector can be maintained. Also, an electrically conductive state can be maintained between attached current collector elastic pieces and electrodes through the electrically conductive adhesive layer.

In addition, the present invention comprises the adhesion step for adhering the elastic pieces of the current collector and the electrodes of the individual fuel cells using adhesive, with the current collector attached to the cell array. Therefore at the time of manufacture, elastic pieces, including those making partial contact with electrodes, can be physically affixed to the electrodes using electrically conductive adhesive so that conductivity is secured via adhesive between elastic pieces and electrodes. Also, the adhesive force of the adhesive compensates for the amount of reduction in the elastic force of elastic pieces during operation, therefore even if there is a loss in the elastic force of elastic pieces, the elastic pieces do not move relative to the electrode, and a conductive state can be secured between elastic pieces and electrodes.

Moreover, in the present invention the electrodes of the individual fuel cells are formed of the same porous material as fuel electrodes or air electrodes, thus simplifying the manufacture of individual fuel cells. Also, in the present invention, by applying electrically conductive adhesive onto electrodes in the application step, the adhesive is disposed to either penetrate pores of the electrodes or block pores of the electrodes. Therefore the electrical conductivity of electrodes of the porous material can be improved. Also, because the contact surface area between elastic pieces and electrodes is substantially increased by the filling of electrode pores with electrically conductive adhesive, electrical resistance between elastic pieces and electrodes can be reduced. Thus in the present invention the electrical conductivity between the current collector and the electrodes of the individual fuel cells can be increased.

In the present invention the adhesive preferably includes granular electrically conductive material.

In the invention thus constituted, the adhesive contains granular electrically conductive material, making it easy for the granular electrically conductive material to penetrate into electrode pores and to increase the electrical conductivity of all or at least the surface layer portion of the electrodes, which are porous bodies. The grain size of the electrically conductive material is preferably about the same as, or less than, the pore diameter of the porous body pores.

The present invention preferably comprises a densifying step for forming a densified layer of the adhesive by sintering the granular electrically conductive material of the adhesive after the application step.

The present invention comprises, after the application step, a densifying step for sintering the adhesive to densify the adhesive, so that electrically conductive material penetrating into electrode pores solidifies after passing through a partially molten state in the pores. The electrically conductive pathway in the electrode pores is in this way substantially expanded, allowing electrodes to be used as high conductivity and densified interconnectors.

In the present invention the densifying step is preferably executed after the attaching step.

In the invention thus constituted the densifying step for adhesive is carried out after the attaching step for attaching the current collector to the cell array, therefore the adhesive can be sintered with the adhesive held under pressure by the elastic force of the elastic pieces. Hence the density of adhesive disposed in the electrically conductive pathway increases in the adhesive locations under the pressure of the elastic pieces, further improving electrical conductivity.

The present invention thus has excellent practical application, being capable of good workability, of achieving increased affixing strength between elastic pieces and electrodes, and of preventing poor conductivity between elastic pieces and electrodes associated with a drop in elastic force of elastic pieces caused by a high temperature environment during operation.

Effect of the Invention

According to the solid oxide fuel cell device and method for manufacturing the same of the present invention, damage to electrodes of individual fuel cells can be prevented, and an electrical connection between individual fuel cells and the current collector can be secured.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1: An overview diagram showing a solid oxide fuel cell (SOFC) device according to an embodiment of the present invention.

FIG. 2: A cross section of an individual fuel cell housing container built into the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 3: A cross section showing an exploded view of the main members of the individual fuel cell housing container built into the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 4: A cross section showing an expanded view of the exhaust collection chamber built into the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 5: A cross section through V-V in FIG. 2.

FIG. 6: (a) A cross section showing an expanded view of the bottom end portion of an individual fuel cell on which the bottom end is used as a cathode; and (b) a cross section showing an expanded view of the bottom end portion of an individual fuel cell on which the bottom end is used as an anode.

FIG. 7: An explanatory figure of a current collector used in the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 8: An explanatory figure of a step in a manufacturing process for the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 9: An explanatory figure of a step in a manufacturing process for the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 10: An explanatory figure of a current collector affixing method pertaining to a first embodiment in a manufacturing process for the solid oxide fuel cell device according to an embodiment of the invention.

FIG. 11: A flowchart of the current collector affixing method pertaining to the first embodiment.

FIG. 12: An explanatory figure showing the state in which the current collector is affixed to the individual fuel cell in the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 13: A flowchart of a current collector affixing method pertaining to a second embodiment in a manufacturing process for the solid oxide fuel cell device according to an embodiment of the present invention.

FIG. 14: An explanatory figure of a current collector affixing method pertaining to a third embodiment in a manufacturing process for the solid oxide fuel cell device according to an embodiment of the invention.

FIG. 15: A flowchart of a current collector affixing method pertaining to the third embodiment.

FIG. 16: An explanatory figure of a current collector affixing method pertaining to a fourth embodiment in a manufacturing process for the solid oxide fuel cell device according to an embodiment of the invention.

FIG. 17: A flowchart of a current collector affixing method pertaining to the fourth embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, referring to the attached drawings, we discuss a solid oxide fuel cell (SOFC) device according to an embodiment of the present invention.

FIG. 1 is an overview diagram showing a solid oxide fuel cell (SOFC) device according to an embodiment of the present invention. As shown in FIG. 1, the solid oxide fuel cell (SOFC) device of this embodiment of the present invention is furnished with a fuel cell module 2 and an auxiliary unit 4.

Fuel cell module 2 is furnished with a housing 6, and a fuel cell housing container 8 is formed within this housing 6, mediated by heat storage material 7. A generating chamber 10 is formed on the interior of this fuel cell housing container 8; a plurality of individual fuel cells 16 are concentrically disposed within this generating chamber 10, and the generating reaction between fuel gas and air, which is the oxidizing gas, is carried out by these individual fuel cells 16.

Exhaust collection chamber 18 is attached to the top end portion of each fuel cell 16. Residual fuel (off-gas), unused for the generating reaction and remaining in each fuel cell 16 is collected in the exhaust collection chamber 18 attached to the top end portion and flows out of the plurality of jet openings placed in the ceiling surface of exhaust collection chamber 18. Outflowing fuel is combusted in the generating chamber 10 using remaining air not used for generation, thereby producing exhaust gas.

Next, auxiliary unit 4 is furnished with a pure water tank 26 for holding water from a municipal or other water supply source 24 and filtering it into pure water, and a water flow rate regulator unit 28 (a “water pump” or the like driven by a motor) for regulating the flow rate of water supplied from this pure tank. Also, auxiliary unit 4 comprises a fuel blower 38 (a motor-driven “fuel pump” or the like), being a fuel supply device, for regulating the flow rate of hydrocarbon raw fuel gas supplied from fuel supply source 30, such as municipal gas.

Note that raw fuel gas which has passed through fuel blower 38 is directed into fuel cell holding container 8 through a desulfurizer 36 disposed inside fuel cell module 2, a heat exchanger 34, and an electromagnetic valve 35. The desulfurizer 36 is disposed in a ring shape around fuel cell housing container 8, and operates to remove sulfur from raw fuel gas. Heat exchanger 34 is provided to prevent the inflow of high temperature raw fuel gas, the temperature of which has risen in the desulfurizer 36, from flowing directly into electromagnetic valve 35 and degrading electromagnetic valve 35. Electromagnetic valve 35 is provided to stop the supply of raw fuel gas into the fuel cell housing container 8.

Auxiliary unit 4 is furnished with an air flow regulator unit 45 (a motor-driven “air blower” or the like), which is an oxidant gas supply device for regulating the flow rate of air supplied from air supply source 40.

Furthermore, auxiliary unit 4 is furnished with a hot water production device 50 for recovering the heat of exhaust gas from fuel cell module 2. Tap water is supplied to this hot water production device 50; this tap water becomes hot water by the heat of the exhaust gas, and is supplied to a hot water tank in an external hot water device, not shown.

In addition, an inverter 54, which is a power extraction section (electrical power conversion section) for supplying power generated by the fuel cell module 2 to the outside, is connected to fuel cell module 2.

Next, referring to FIGS. 2 and 3, we discuss the internal structure of the fuel cell housing container built into the fuel cell module of the solid oxide fuel cell (SOFC) device according to an embodiment of the present invention.

FIG. 2 is a cross-section of the fuel cell housing container, and FIG. 3 is a cross-section showing a disassembled view of main members of the fuel cell housing container.

As shown in FIG. 2, a plurality of individual fuel cells 16 are concentrically arrayed in the space within fuel cell holding container 8, formed so as to surround it concentrically; represented in order are fuel gas supply flow path 20, being a fuel flow path, exhaust gas discharge flow path 21, and oxidant gas supply flow path 22. Here, exhaust gas discharge flow path 21 and oxidant gas supply flow path 22 function as an oxidant gas flow path for discharging/supplying oxidant gas.

First, as shown in FIG. 2, fuel cell holding container 8 is an approximately cylindrical sealed container; connected to the side surface thereof are an oxidant gas introducing pipe 56, being an oxidant gas inflow port for supplying generating air, and an exhaust gas discharge pipe 58 for discharging exhaust gas. In addition, an ignition heater 62 for igniting residual fuel flowing out from exhaust collection chamber 18 protrudes from the top end surface of fuel cell housing container 8.

As shown in FIGS. 2 and 3, inside cylindrical member 64, being a generating chamber constituent member, outside cylindrical member 66, inside cylindrical container 68, and outside cylindrical container 70 are disposed in that order to surround the periphery of individual fuel cells 16 on the inside of fuel cell holding container 8. The above-described fuel gas supply flow path 20, exhaust gas discharge flow path 21, and oxidant gas supply flow path 22 are flow paths respectively constituted between these cylindrical members and cylindrical containers, and heat is exchanged between adjacent flow paths.

That is, exhaust gas discharge flow path 21 is disposed to surround fuel gas supply flow path 20, and oxidant gas supply flow path 22 is disposed to surround exhaust gas discharge flow path 21. The open space at the bottom end of fuel cell housing container 8 is blocked off by an approximately circular dispersion chamber bottom member 72, which forms the bottom surface of fuel gas dispersion chamber 76 for dispersing fuel into each fuel cell 16.

Inside cylindrical member 64 is an approximately cylindrical empty body, open at its top and bottom ends First affixing member 63, being a dispersion chamber-forming plate, is welded in an airtight manner to the interior wall surface of inside cylindrical member 64. A fuel gas dispersion chamber 76 is defined by the bottom surface of this first affixing member 63, the inside wall surface of inside cylindrical member 64, and the top surface of dispersion chamber bottom member 72. A plurality of insertion holes 63 a, into which individual fuel cells 16 are inserted, are formed on first affixing member 63, and each fuel cell 16 is adhered to first affixing member 63 by ceramic adhesive, with the individual fuel cells 16 inserted into each of the insertion holes 63 a. Thus in the solid oxide fuel cell device 1 of the embodiment, ceramic adhesive is filled into the mutual joining portions between members constituting fuel cell module 2, and with hardening, each of the members is mutually joined in an airtight manner.

Outside cylindrical member 66 is a cylindrical pipe disposed around inside cylindrical member 64, formed to have an approximately similar shape to inside cylindrical member 64 so that an annular flow path is formed between outside cylindrical member 66 and inside cylindrical member 64. In addition, an intermediate cylindrical member 65 is disposed between inside cylindrical member 64 and outside cylindrical member 66. Intermediate cylindrical member 65 is a cylindrical pipe disposed between inside cylindrical member 64 and outside cylindrical member 66; a reforming section 94 is constituted between the outer periphery of inside cylindrical member 64 and the inner periphery of intermediate cylindrical member 65. Also, the annular space between the outer periphery surface of intermediate cylindrical member 65 and the inner periphery surface of outside cylindrical member 66 functions as a fuel gas supply flow path 20. Therefore reforming section 94 and fuel gas supply flow path 20 receive heat from heat generation of individual fuel cells 16 and combustion of residual fuel at the top end of exhaust collection chamber 18. The top end portion of inside cylindrical member 64 and top end portion of outside cylindrical member 66 are joined in an airtight manner by welding, while the top end of fuel gas supply flow path 20 is closed off. Also, the bottom end of intermediate cylindrical member 65 and the outer periphery surface of inside cylindrical member 64 are joined in an airtight manner by welding.

Inside cylindrical container 68 is a cup-shaped member, circular in section, disposed around outside cylindrical member 66, the side surface of which is formed to have an approximately similar shape to outside cylindrical member 66, so that an annular flow path of approximately fixed width is formed between inside cylindrical container 68 and outside cylindrical member 66. This inside cylindrical container 68 is disposed to cover the open portion at the top end of inside cylindrical member 64. The annular space between the outer periphery surface of outside cylindrical member 66 and the inner periphery surface of inside cylindrical container 68 functions as exhaust gas discharge flow path 21 (FIG. 2). This exhaust gas discharge flow path 21 communicates with the space within inside cylindrical member 64 through a plurality of small holes 64 a in the top end portion of inside cylindrical member 64. Exhaust gas discharge pipe 58, being an exhaust gas discharge port, is connected at the lower portion side surface of inside cylindrical container 68, and exhaust gas discharge flow path 21 communicates with exhaust gas discharge pipe 58.

A combustion catalyst 60 and a sheath heater 61 for heating the combustion catalyst is disposed on the bottom portion of exhaust gas discharge flow path 21.

Combustion catalyst 60 is a catalyst filled into the annular space between the outer periphery surface of outside cylindrical member 66 and the inner periphery surface of inside cylindrical container 68, above exhaust gas discharge pipe 58. By passing through combustion catalyst 60, carbon monoxide is removed from exhaust gas descending the exhaust gas discharge flow path 21 to be discharged from exhaust gas discharge pipe 58.

Sheath heater 61 is an electrical heater attached to surround the outer periphery surface of outside cylindrical member 66 at the bottom of combustion catalyst 60. Upon startup of solid oxide fuel cell device 1, combustion catalyst 60 is heated to an activation temperature by energizing sheath heater 61.

Outside cylindrical container 70 is a cup-shaped member, circular in cross section, disposed around inside cylindrical container 68, the side surface of which is formed to have an approximately similar shape to inside cylindrical container 68, so that an annular flow path of approximately fixed width is formed between outside cylindrical container 70 and inside cylindrical container 68. The space between the outer periphery surface of inside cylindrical container 68 and the inner periphery surface of outside cylindrical container 70 functions as oxidant gas supply flow path 22.

Oxidant gas introducing pipe 56 is connected to the lower portion side surface of outside cylindrical container 70; oxidant gas supply flow path 22 communicates with oxidant gas introducing pipe 56.

Dispersion chamber bottom member 72 is an approximately circular plate-shaped member, affixed to the inside wall surface of inside cylindrical member 64 with a ceramic adhesive in an airtight manner. A fuel gas dispersion chamber 76 is thus constituted between first affixing member 63 and dispersion chamber bottom member 72. Also, insertion pipe 72 a for the insertion of bus bars 80 (FIG. 2) is provided at the center of dispersion chamber bottom member 72. Bus bars 80, electrically connected to each individual fuel cell 16, are routed out to the outside of fuel cell housing container 8 through this insertion pipe 72 a. Ceramic adhesive is filled into insertion pipe 72 a, thereby securing the airtightness of fuel gas dispersion chamber 76. In addition, heat storage material 72 b (FIG. 2) is disposed around the periphery of insertion pipe 72 a.

An oxidant gas injecting pipe 74 for injecting generating air, circular in cross section, is attached so as to hang down from the ceiling surface of inside cylindrical container 68. This oxidant gas injecting pipe 74 then extends in the vertical direction on the center axial line of inside cylindrical container 68, and each fuel cell 16 is disposed on concentric circles around oxidant gas injecting pipe 74. By attaching the top end of oxidant gas injection pipe 74 to the ceiling surface of inside cylindrical container 68, oxidant gas supply flow path 22, formed between inside cylindrical container 68 and external cylindrical container 70, is made to communicate with oxidant gas injection pipe 74. Air supplied via oxidant gas supply flow path 22 is injected downward from the tip of oxidant gas injecting pipe 74, hitting the top surface of first affixing member 63 and spreading to the entire interior of generating chamber 10.

Fuel gas dispersion chamber 76 is a cylindrical airtight chamber constituted between first affixing member 63 and dispersion chamber bottom member 72, on the top surface of which each of the fuel cells 16 are stood in close proximity. The inside fuel electrode of each individual fuel cell 16 attached to the top surface of first affixing member 63 communicates with the interior of fuel gas dispersion chamber 76. The bottom end portion of each individual fuel cell 16 penetrates the insertion holes 63 a in first affixing member 63 and projects into fuel gas dispersion chamber 76, so that each fuel cell 16 is affixed by adhesion to first affixing member 63.

As shown in FIG. 2, a plurality of small holes 64 b are provided on inside cylindrical member 64 at a position below first affixing member 63. The space between the outer periphery of inside cylindrical member 64 and the inner periphery of intermediate cylindrical member 65 communicates with the inside of fuel gas dispersion chamber 76 through a plurality of small holes 64 b. Supplied fuel first rises through the space between the inner periphery of outside cylindrical member 66 and the outer periphery of intermediate cylindrical member 65, then descends through the space between the outer periphery of inside cylindrical member 64 and the inner periphery of intermediate cylindrical member 65, flowing into fuel gas dispersion chamber 76 through a plurality of small holes 64 b. Fuel gas which has flowed into fuel gas dispersion chamber 76 is distributed to fuel electrode of each individual fuel cell 16 attached to the ceiling surface of fuel gas dispersion chamber 76 (first affixing member 63).

In addition, the bottom end portions of the individual fuel cells 16 projecting inside fuel gas dispersion chamber 76 are electrically connected to bus bars 80 inside fuel gas dispersion chamber 76, and power is extracted to the outside through electrical conductor conduit 72 a. Bus bars 80 are elongated metal conductors for extracting power produced by each fuel cell 16 to the outside of fuel cell housing container 8, affixed to insertion pipe 72 a of dispersion chamber bottom member 72 through glass 78. Bus bars 80 are electrically connected to a current collector 82 attached to each fuel cell 16 on the interior of fuel gas dispersion chamber 76. Bus bars 80 are also connected on the outside of fuel cell housing container 8 to the inverter 54 (FIG. 1). Note that current collector 82 is also attached to the top end portions of each fuel cell 16 projecting into exhaust collection chamber 18 (FIG. 4). A plurality of individual fuel cells 16 are electrically connected in parallel by these current collectors 82 at the top and bottom end portions, and a plurality of sets of parallel-connected individual fuel cells 16 are electrically connected in series, with both ends of these series connections connected to respective bus bars 80.

Next, referring to FIGS. 4 and 5, we explain the constitution of the exhaust collection chamber.

FIG. 4 is a cross section showing an expanded view of the exhaust collection chamber part; FIG. 5 is a cross section through V-V in FIG. 2.

As shown in FIG. 4, exhaust collection chamber 18 is a chamber with a donut-shaped cross section attached to the top end portion of each fuel cell 16; the oxidant gas injection pipe 74 penetrates and extends at the center of this exhaust collection chamber 18.

As shown in FIG. 5, three stays 64 c for supporting exhaust collection chamber 18 are attached at equal spacing on the inside wall surface of inside cylindrical member 64. As shown in FIG. 4, stays 64 c are small tabs of bent thin metal plate; by mounting exhaust collection chamber 18 on each of the stays 64 c, exhaust collection chamber 18 is positioned concentrically relative to inside cylindrical member 64. Thus the gap between the outer periphery of exhaust collection chamber 18 and the inner periphery of inside cylindrical member 64, and the gap between the inner periphery of exhaust collection chamber 18 and the outer periphery of oxidant gas injecting pipe 74, are made uniform around the entire circumference (FIG. 5).

Exhaust collection chamber 18 is constituted so that collection chamber upper member 18 a and collection chamber lower member 18 b are joined in an airtight manner.

Collection chamber lower member 18 b is a circular plate-shaped member open at the top, at the center of which a cylindrical portion is formed to allow the penetration of oxidant gas injection pipe 74.

Collection chamber upper member 18 a is a circular plate-shaped member open at the bottom, at the center of which an open portion is formed to allow the penetration of oxidant gas injection pipe 74. Collection chamber upper member 18 a has a shape capable of insertion into the doughnut shaped cross-sectional region which opens at the top of collection chamber lower member 18 b.

A ceramic adhesive is filled into the gap between the inner periphery of the perimeter wall of collection chamber lower member 18 b and the outer periphery surface of collection chamber upper member 18 a, and hardened, securing the airtightness of this joint portion.

A large diameter seal ring 19 a is disposed on the ceramic adhesive layer formed by the ceramic adhesive filled into this joint portion, covering the ceramic adhesive layer. Large diameter seal ring 19 a is an annular thin sheet, disposed to cover the filled-in ceramic adhesive layer after the ceramic adhesive is filled, and affixed to exhaust collection chamber 18 by the hardening of the adhesive.

On the other hand, a ceramic adhesive is filled and hardened between the outer periphery surface of the cylindrical portion at the center of collection chamber lower member 18 b and the opening edge at the center of collection chamber upper member 18 a, securing the airtightness of this joint portion. A small diameter seal 19 b is disposed on the ceramic adhesive layer formed by the ceramic adhesive filled into this joint portion, covering the ceramic adhesive layer. The small diameter seal 19 b is an annular thin sheet, disposed to cover the filled-in ceramic adhesive layer after the ceramic adhesive is filled, and affixed to exhaust collection chamber 18 by the hardening of the adhesive.

A plurality of round insertion holes 18 c are disposed on the bottom surface of collection chamber lower member 18 b. The top end portions of each fuel cell 16 respectively penetrate each of the insertion holes 18 c, and each fuel cell 16 penetrates each of the insertion holes 18 c and extends. As ceramic adhesive is flowed onto the bottom surface of collection chamber lower member 18 b, which is penetrated by individual fuel cells 16, and hardened, the gap between the outer periphery of each individual fuel cell 16 and the insertion holes 18 c is filled in an airtight manner, and each fuel cell 16 is affixed to collection chamber lower member 18 b.

Moreover, a circular thin-plate cover member 19 c is disposed on the ceramic adhesive poured onto the bottom surface of collection chamber lower member 18 b, and affixed to collection chamber lower member 18 b by the hardening of the ceramic adhesive. A plurality of insertion holes are formed in cover member 19 c at the same positions as each of the insertion holes 18 c in collection chamber lower member 18 b, and the top end portions of each fuel cell 16 penetrate and extend through this ceramic adhesive layer and cover member 19 c.

At the same time, a plurality of jet ports 18 d for jetting collected fuel gas are provided on the ceiling surface of exhaust collection chamber 18 (FIG. 5). Each of the jet ports 18 d is disposed in a circle on collection chamber upper member 18 a. Fuel remaining unused for electrical generation flows out from the top end of each fuel cell 16 into exhaust collection chamber 18, and fuel collected inside exhaust collection chamber 18 flows out from jet ports 18 d, where it is combusted.

Next, referring to FIG. 2, we discuss a structure for reforming raw fuel gas supplied from fuel supply source 30.

First, a vaporizing section 86 for vaporizing water for steam reforming is provided at the lower portion of fuel gas supply flow path 20, which is constituted by the space between inside cylindrical member 64 and outside cylindrical member 66. Vaporizing section 86 is formed of ring-shaped tilted plate 86 a attached to the bottom inside circumference of outside cylindrical member 66, and water supply pipe 88. Vaporizing section 86 is also disposed above exhaust gas discharge pipe 58, which discharges exhaust gas, and below oxidant gas introducing pipe 56 for introducing electrical generating air. Tilted plate 86 a is thin metal plates formed in a ring shape, the outside perimeter edge of which is attached to the inside wall surface of outside cylindrical member 66. The inside perimeter edge thereof, on the other hand, is positioned above the outside perimeter edge, and a gap is provided between the inside perimeter edge of tilted plate 86 a and the outside wall surface of inside cylindrical member 64.

Water supply pipe 88 is a pipe extending from the bottom end of inside cylindrical member 64 in a vertical direction within fuel gas supply flow path 20; water for steam reforming supplied from water flow rate regulator unit 28 is supplied to vaporizing section 86 through water supply pipe 88. The top end of water supply pipe 88 penetrates tilted plate 86 a and extends up to the top surface side of tilted plate 86 a; water supplied to the top surface side of tilted plate 86 a accumulates between the top surface of tilted plate 86 a and the inside wall surface of outside cylindrical member 66. Water supplied to the top surface of tilted plate 86 a is vaporized there to produce steam.

Also, a fuel gas introducing portion for introducing raw fuel gas into fuel gas supply flow path 20 is placed below vaporizing section 86. Raw fuel gas fed from fuel blower 38 is introduced into fuel gas supply flow path 20 via a fuel gas supply pipe 90. Fuel gas supply pipe 90 is a pipe extending vertically inside fuel gas supply flow path 20 from the bottom end of inside cylindrical member 64.

The top end of fuel gas supply pipe 90 is positioned below tilted plate 86 a. Raw fuel gas fed from fuel blower 38 is introduced at the bottom side of tilted plate 86 a and rises to the top side of tilted plate 86 a as its flow path is constricted by the inclination of tilted plate 86 a. Raw fuel gas rising to the top side of tilted plate 86 a rises together with the steam produced by vaporizing section 86.

A fuel gas supply flow path partition 92 is provided above vaporizing section 86 inside fuel gas supply flow path 20. Fuel gas supply flow path partition 92 is an annular metal plate disposed to separate into top and bottom portions the annular space between the inner periphery of outside cylindrical member 66 and the outer periphery of intermediate cylindrical member 65. A plurality of equally spaced injection ports 92 a are provided in a circle on this fuel gas supply flow path partition 92, and the spaces above and below fuel gas supply flow path partition 92 communicate by means of these injection ports 92 a. Raw fuel gas introduced from fuel gas supply pipe 90 and steam produced by vaporizing section 86 are first pooled in the space on the bottom side of fuel gas supply flow path partition 92, then passed through each of injection ports 92 a and injected into the space on the top side of fuel gas supply flow path partition 92. When injected into the wide space on the top side of fuel gas supply flow path partition 92 from each of the injection ports 92 a, the raw fuel gas and steam are suddenly decelerated and here sufficiently mixed.

In addition, reforming section 94 is provided at the top portion of the annular space between the inner periphery of intermediate cylindrical member 65 and the outer periphery of inside cylindrical member 64. Reforming section 94 is disposed to surround the top portion of each fuel cell 16 and the periphery of the exhaust collection chamber 18 at the top thereof. Reforming section 94 comprises a catalyst holding plate (not shown) attached to the outer wall surface of inside cylindrical member 64, and a reforming catalyst 96 held in place thereby.

Thus when raw fuel gas and steam, mixed in the space on the top side of fuel gas supply flow path partition 92, make contact with the reforming catalyst 96 filled into reforming section 94, the steam reforming reaction SR shown by Eq. (1) proceeds inside reforming section 94. CmHn+xH₂O→aCO₂ +bCO+cH₂  (1)

Fuel gas reformed in reforming section 94 flows downward in the space between the inner periphery of intermediate cylindrical member 65 and the outer periphery of inside cylindrical member 64, then flows into fuel gas dispersion chamber 76 and is supplied to each fuel cell 16. The steam reforming reaction SR is an endothermic reaction, however the heat required for the reaction is supplied by the combustion heat of off-gas flowing out from exhaust collection chamber 18, and the emitted heat produced in each fuel cell 16.

Next, referring to FIG. 6, we explain individual fuel cells 16.

In the solid oxide fuel cell device 1 according to an embodiment of the present invention, cylindrical lateral band cells using solid oxides are employed for fuel cells 16. A plurality of single cells 16 a are arranged in lateral band form on each individual fuel cell 16, and each individual fuel cell 16 is constituted by electrically connecting these single cells together in series. Each fuel cell 16 comprises an anode (positive electrode) at one end and a cathode (negative electrode) at the other end; of the plurality of individual fuel cells 16, half are disposed so that the top end is an anode and the bottom end is a cathode, while the other half are disposed so that the top end is a cathode and the bottom end is an anode.

FIG. 6(a) is a cross section showing an expanded view of the bottom end portion of an individual fuel cell 16 on which the bottom end is used as a cathode; and FIG. 6(b) is a cross section showing an expanded view of the bottom end portion of an individual fuel cell 16 on which the bottom end is used as an anode.

As shown in FIG. 6, an individual fuel cell 16 is formed of an elongated cylindrical porous support body 97, and a plurality of layers formed in a lateral band shape on the outside of this porous support body 97. In the following order, starting from the inside, fuel electrode 98, reaction suppression layer 99, solid electrolyte layer 100, and air electrode 101 are respectively formed in a lateral band shape surrounding porous support body 97. Therefore fuel gas supplied via fuel gas dispersion chamber 76 flows into the porous support body 97 of each individual fuel cell 16, and air jetted from oxidant gas injection pipe 74 flows to the outside of air electrode 101. Each of the single cells 16 a formed on the individual fuel cells 16 is comprised of one set of a fuel electrode 98, a reaction suppression layer 99, a solid electrolyte layer 100, and an air electrode 101. The fuel electrode 98 in a single cell 16 a is electrically connected to the air electrode 101 of the adjacent single cell 16 a through interconnector layer 102. In this manner, the plurality of single cells 16 a formed on a single individual fuel cell 16 are electrically connected in series.

As shown in FIG. 6(a), electrode layer 103 a is formed on the outer periphery of porous support body 97 at the cathode-side end portion of individual fuel cells 16, and a lead film layer 104 a is formed on the outside of this electrode layer 103 a. In the cathode-side end portion, the air electrode 101 of single cells 16 a positioned at the end portions and electrode layer 103 a are electrically connected by interconnector layer 102. The electrode layer 103 a and the lead film layer 104 a are formed to penetrate first affixing member 63 at the end portion of individual fuel cells 16, and to protrude further downward than first affixing member 63. Electrode layer 103 a is formed further down than lead film layer 104 a, and current collector 82 is electrically connected to electrode layer 103 a exposed to the outside. Thus air electrodes 101 of single cells 16 a positioned at the end portions are connected to current collector 82 through interconnector layer 102 and electrode layer 103 a, and electrical current flows as shown by the arrow in the diagram. Ceramic adhesive is filled into the gap between the edge of the insertion holes 63 a on first affixing member 63 and lead film layer 104 a, and individual fuel cells 16 are affixed to first affixing member 63 on the outer periphery of lead film layer 104 a.

As shown in FIG. 6(b), fuel electrode layer 98 of a single cell 16 a positioned on the end portion extends at the anode-side end portion of individual fuel cells 16, and the extending portion of fuel electrode layer 98 functions as electrode layer 103 b. Lead film layer 104 b is formed on the outside of electrode layer 103 b.

The electrode layer 103 b and the lead film layer 104 b are formed to penetrate first affixing member 63 at the end portion of individual fuel cells 16, and to protrude further downward than first affixing member 63.

Electrode layer 103 b is formed further down than lead film layer 104 b, and current collector 82 is electrically connected to electrode layer 103 b exposed to the outside. Thus the fuel electrode 98 of single cell 16 a positioned at the end portion is connected to current collector 82 through integrally formed electrode layer 103 b, and electrical current flows as shown by the arrow in the diagram. Ceramic adhesive is filled into the gap between the edge of the insertion holes 63 a on first affixing member 63 and lead film layer 104 b, and individual fuel cells 16 are affixed to first affixing member 63 on the outer periphery of lead film layer 104 b.

In FIGS. 6(a) and (b) we explained the constitution of the bottom end portion of individual fuel cells 16; the top end portion of individual fuel cells 16 is the same. Note that at the top end portion, individual fuel cells 16 are affixed to the collection chamber lower member 18 b of exhaust collection chamber 18; the constitution of the affixing portion is the same as the affixing to the first affixing member 63 at the bottom end portion thereof.

Next we explain the constitution of porous support body 97 and of each layer.

In the embodiment, porous support body 97 is formed by extruding and sintering a mixture of forsterite powder and a binder.

In the embodiment, fuel electrode 98 is an electrically conductive thin film comprised of a mixture of NiO powder and 10YSZ (10 mol % Y₂O₃-90 mol % ZrO₂) powder.

In the embodiment, reaction suppression layer 99 is a thin film comprising cerium compound oxide (LDC 40; i.e., 40 mol % La₂O₃-60 mol % CeO₂) or the like, by which chemical reactions between fuel electrode 98 and solid electrolyte layer 100 are suppressed. In the embodiment, solid electrolyte layer 100 is a thin film formed of an LSGM powder having a composition of La_(0.9)Sr_(0.1)Ga_(0.8)Mg_(0.2)O₃. Electrical energy is produced by the reaction between oxide ions and hydrogen or carbon monoxide through this solid electrolyte layer 100.

In the embodiment, air electrode 101 is an electrically conductive thin film formed of a powder having a composition of La_(0.6)Sr_(0.4)Co_(0.8)Fe_(0.2)O₃.

In the embodiment, interconnector layer 102 is an electrically conductive thin film formed of SLT (lanthanum doped strontium titanate). Adjacent single cells 16 a on individual fuel cells 16 are connected via interconnector layer 102.

In the embodiment, electrode layers 103 a and 103 b are formed of the same material as fuel electrode 98.

In the embodiment, lead film layers 104 a and 104 b are formed of the same material as solid electrolyte layer 100.

Note that lead film layers 104 a, 104 b are dense layers, the same as solid electrolyte layer 100, therefore airtightness is secured by adhesion with the ceramic adhesive.

In this embodiment electrode layers 103 a and 103 b are formed of the same porous material as fuel electrode layer 98, but without limitation thereto electrode layers 103 a and 103 b may also be formed of other electrically conductive porous materials containing the same porous material as reaction suppression layer 99 or air electrode layer 101. For example, the air electrode layer 101 of single cell 16 a formed at a position closest to the end portion of individual fuel cells 16 may be further extended in the end portion direction, and the extended portion thereof used as an electrode layer.

Next, referring to FIG. 7, we explain the current collector.

FIG. 7 is a diagram viewed from above current collector 82. FIGS. 7(a) and 7(b) respectively depict the current collectors 82A, 82B attached to the top end portion and the bottom end portion of individual fuel cells 16. FIG. 7(c) is an expanded view of the attaching holes 84 formed in current collectors 82A, 82B.

Current collector 82 is formed by machining a thin sheet material with elasticity and electrical conductivity. In this embodiment, it is formed using a nickel plate material.

Current collector 82A comprises two approximately semicircular current collector plates 83 a, 83 b. By disposing these current collector plates 83 a, 83 b adjacently, current collector 82A has an approximately circular outer shape, and a circular opening is formed at the center thereof for inserting oxidant gas injection pipe 74.

Current collector 82B comprises one approximately semicircular current collector plate 83 c and two approximately quadrant-shaped current collector plates 83 d, 83 e. By disposing these current collector plates 83 c-83 e adjacently, current collector 82B has an approximately circular outer shape, and a circular opening is formed at the center thereof. Connecting portions 83 f, 83 g for connecting bus bars 80 are provided on current collector plates 83 d, 83 e.

In the present embodiment, a plurality of (76 in this example) individual fuel cells 16 are divided into four groups of 19. As shown in FIG. 2, when current collector 82 is connected to the top end and bottom end portions of individual fuel cells 16, the individual fuel cells 16 in each group are connected in parallel through current collector 82, and the four groups are connected in series. That is, if the current collector plate 83 d connected to one of the bus bars 80 is assumed to be an anode (positive electrode), for example, the bottom half of current collector plate 83 a becomes a cathode (negative electrode) through the first group of individual fuel cells 16 connected to current collector plate 83 d, the top half becomes an anode, and the left half of current collector plate 83 c becomes a cathode through the second group of individual fuel cells 16. Similarly, the right half of current collecting plate 83 c becomes an anode, the top half of current collector plate 83 b becomes a cathode through the third group of individual fuel cells 16, and finally the current collector plate 83 e connected to the other bus bar 80 becomes a cathode through the fourth group of individual fuel cells 16.

As shown in FIG. 7(c), the attaching holes 84 in each current collector plate are formed by the machining of radial notches. One attaching hole 84 is formed by 6 notch lines. An imaginary line 84 b connecting both ends of the notch lines forms a circle larger than the outside dimension (imaginary line 84 c) of individual fuel cell 16. Using these notch lines, 12 elastic pieces 84 a are formed so as to extend toward the center of the circle (toward the inside of the diameter) from the imaginary line 84 b (i.e., the inside perimeter edge of attaching hole 84).

Each elastic piece 84 a is approximately fan shaped, tapering toward the tip, and the tip portion thereof can elastically bend relative to the base end portion (imaginary line 84 b). Therefore when an individual fuel cell 16 is inserted into an attaching hole 84, the tip portion of elastic piece 84 a contacts the outer periphery surface of the individual fuel cell 16 and bends along its outer periphery surface, and elastic piece 84 a elastically engages the individual fuel cell 16. When an individual fuel cell 16 is inserted into the current collector to a predetermined position, the current collector is held to the individual fuel cell 16 by the elastic force of elastic pieces 84 a.

Next, referring to FIGS. 1 and 2, we explain the operation of solid oxide fuel cell device 1.

First, in the startup step of the solid oxide fuel cell device 1, fuel blower 38 is started and supply of fuel is commenced, while sheath heater 61 is also energized. By energizing sheath heater 61, the combustion catalyst 60 disposed above sheath heater 61 is heated, and the vaporization section 86 disposed inside is also heated. Fuel supplied by fuel blower 38 flows from fuel gas supply pipe 90 via desulfurizer 36, heat exchanger 34, and electromagnetic valve 35 into the interior of fuel cell housing container 8. In-flowing fuel, after rising up to the top end within fuel gas supply flow path 20, drops down within reforming section 94, then through small holes 64 b placed on the bottom portion of inside cylindrical member 64, and into fuel gas dispersion chamber 76. Note that immediately after the startup step of the solid oxide fuel cell device 1, because the temperature of reforming catalyst 96 in reforming section 94 has not risen sufficiently, no fuel reforming is performed.

Fuel gas which has flowed into fuel gas dispersion chamber 76 flows through the inside (the fuel electrode side) of each fuel cell 16 attached to first affixing member 63 of fuel gas dispersion chamber 76, then into exhaust collection chamber 18. Note that immediately after the startup of the solid oxide fuel cell device 1, the temperature of each fuel cell 16 has not risen sufficiently, nor is power being extracted to inverter 54, therefore no electrical generating reaction occurs.

Fuel flowing into exhaust collection chamber 18 is jetted out from jet ports 18 d in exhaust collection chamber 18. Fuel jetted from jet ports 18 d is ignited by ignition heater 62 and combusted. Reforming section 94, disposed around exhaust collection chamber 18, is heated by this combustion. Exhaust gas produced by combustion flows into exhaust gas discharge flow path 21 through small holes 64 a formed in the top portion of inside cylindrical member 64. High temperature exhaust gas descends within exhaust gas discharge flow path 21, heating fuel flowing in the fuel gas supply flow path 20 disposed on the inside thereof and generating air flowing in the oxidant gas supply flow path 22 disposed on the outside thereof. In addition, exhaust gas passes through combustion catalyst 60 disposed within exhaust gas discharge flow path 21, whereby carbon monoxide is removed, then passes through exhaust gas discharge pipe 58 to be discharged from fuel cell housing container 8.

When vaporization section 86 is heated by exhaust gas and sheath heater 61, water for steam reforming supplied to vaporization section 86 is vaporized and steam is produced. Water for steam reforming is supplied by water flow rate regulator unit 28 to vaporization section 86 in fuel cell housing container 8 via water supply pipe 88. The steam produced by vaporization section 86 and fuel supplied through fuel gas supply pipe 90 are first held in the space on the bottom side of fuel gas supply flow path partition 92 inside fuel gas supply flow path 20, then injected from a plurality of injection ports 92 a formed in fuel gas supply flow path partition 92. Fuel and steam injected with high force from injection ports 92 a are well blended by being decelerated in the space on the top side of fuel gas supply flow path partition 92.

Blended fuel and steam rise up within fuel gas supply flow path 20 and flow into reforming section 94. In a state whereby the reforming catalyst 96 of reforming section 94 has risen to a temperature at which reforming is possible, a steam reforming reaction occurs when the mixed gas of fuel and steam passes through reforming section 94, whereby mixed gas is reformed into a hydrogen-rich fuel. Reformed fuel passes through small holes 64 b and flows into fuel gas dispersion chamber 76. A large number of small holes 64 b are formed around fuel gas dispersion chamber 76, and sufficient capacity is thus assured for fuel gas dispersion chamber 76, therefore reformed fuel flows in uniformly to the individual fuel cells 16 projecting into fuel gas dispersion chamber 76.

In the meantime air, which is the oxidant gas supplied by air flow regulator unit 45, flows into oxidant gas supply flow path 22 through oxidant gas introducing pipe 56. Air flowing into oxidant gas supply flow path 22 rises up in oxidant gas supply flow path 22 as it is heated by the exhaust gas flowing on the inside thereof. Air rising in oxidant gas supply flow path 22 is gathered at the center of the top end portion in fuel cell housing container 8 and flows into oxidant gas injection pipe 74, which communicates with oxidant gas supply flow path 22. Air flowing into oxidant gas injection pipe 74 is injected from the bottom end thereof into generating chamber 10; the injected air then hits the top surface of first affixing member 63 and spreads throughout the entire generating chamber 10. Air flowing into generating chamber 10 rises up through the gap between the outer periphery wall of exhaust collection chamber 18 and the inner periphery wall of inside cylindrical member 64, and through the gap between the inner periphery wall of exhaust collection chamber 18 and the outer periphery of oxidant gas injection pipe 74.

At this point, a portion of the air flowing over the exterior (air electrode side) of each fuel cell 16 is used for the generating reaction. In addition, a portion of the air which has risen at the top of exhaust collection chamber 18 is used to combust the fuel jetted from jet ports 18 d of exhaust collection chamber 18. Exhaust gas produced by combustion and air not used for electrical generation or combustion passes through small holes 64 a and flows into exhaust gas discharge flow path 21. Exhaust gas and air flowing into exhaust gas discharge flow path 21 is discharged after carbon monoxide is removed by combustion catalyst 60.

Thus when each fuel cell 16 rises to approximately 650° C., at which generation is possible, and reformed fuel flows into the interior (fuel electrode side) of each fuel cell 16 and air flows on the outside (air electrode side) thereof, electromotive force is generated by a chemical reaction. In this state, when inverter 54 is connected to bus bars 80, routed out from fuel cell housing container 8, electric power is extracted from each fuel cell 16 and electricity is generated.

In solid oxide fuel cell device 1 of the embodiment, generating air is jetted from the oxidant gas jetting pipe 74 disposed at the center of generating chamber 10 and rises up in generating chamber 10 through the uniform gap between exhaust collection chamber 18 and inside cylindrical member 64 and the uniform gap between exhaust collection chamber 18 and oxidant gas jetting pipe 74. Therefore the flow of air inside generating chamber 10 is essentially a fully axially symmetrical flow, and air flows uniformly around each individual fuel cell 16. Temperature differences between individual fuel cells 16 are thereby suppressed, and a uniform electromotive force can be produced by each individual fuel cell 16.

Next, referring to FIGS. 2-4, 8 and 9, we explain a method for manufacturing the solid oxide fuel cell device 1 according to an embodiment of the present invention.

First, inside cylindrical member 64, intermediate cylindrical member 65, outside cylindrical member 66, and first affixing member 63 are assembled by welding into a single unit (see FIG. 3). Also, reforming catalyst 96 is filled into the reforming section 94 provided between inside cylindrical member 64 and intermediate cylindrical member 65. Furthermore, water supply pipe 88 and fuel gas supply pipe 90 are also attached by welding.

Next, one end portion of individual fuel cells 16 is inserted into insertion holes 63 a of first affixing member 63, and individual fuel cells 16 are positioned by a fixture or the like relative to first affixing member 63. Following this, the collection chamber lower member 18 b, being a second affixing member, is disposed on the other end portion side of the positioned individual fuel cells 16.

After thus pouring ceramic adhesive onto collection chamber lower member 18 b and disposing cover member 19 c with each fuel cell 16 in a positioned state, the ceramic adhesive is hardened by heating in a drying oven. Ceramic adhesive layer 118 (see FIG. 2) is thus formed. The cell bonding portion between individual fuel cells 16 and collection chamber lower member 18 b is bonded in an airtight manner by ceramic adhesive layer 118.

Note that each fuel cell 16 is adhered by ceramic adhesive at the lead film layers 104 a and 104 b thereof (see FIG. 6).

In the heating step for ceramic adhesive, the temperature inside the drying oven is raised from room temperature to approximately 60° C. in approximately 120 minutes, then raised to approximately 80° C. in approximately 20 minutes, then maintained at approximately 80° C. for approximately 60 minutes. After maintaining the temperature at approximately 80° C., the temperature inside the drying oven is returned to room temperature in approximately 30 minutes.

By this heating step, the ceramic adhesive is hardened to a state at which subsequent manufacturing steps can be implemented. In subsequent steps, the ceramic adhesive is hardened by performing a second heating step to a state able to withstand the temperature rise occurring at the startup step of the solid oxide fuel cell device 1.

Next, the assembly is vertically inverted, ceramic adhesive is poured onto the first affixing member 63 on which the tips of each fuel cell 16 are projecting, and the cover member 67 is disposed, after which the ceramic adhesive is hardened by implementing the above-described heating step in the drying oven. Ceramic adhesive layer 122 (see FIG. 2) is thus formed. The cell bonding portion between individual fuel cells 16 and first affixing member 63 is bonded in an airtight manner by ceramic adhesive layer 122.

Next, as shown in FIG. 8, current collector 82 is attached to the tip portions of the individual fuel cells 16 projecting from first affixing member 63 (the bottom end portions when not vertically inverted) and this current collector 82 is connected to bus bars 80. Relative to the cell array comprised of a plurality of individual fuel cells 16, current collector 82 is positioned such that each of the attaching holes 84 is axially above corresponding individual fuel cell 16. Current collector 82 is pressed onto the cell array from above by a predetermined pressing force. Thus the end portions of individual fuel cells 16 are inserted into attaching holes 84, and current collector 82 is attached to the cell array by the elastic force of elastic pieces 84 a of attaching holes 84.

Next, dispersion chamber bottom member 72 is attached to the assembly. In addition, ceramic adhesive is filled into the annular gap between the outer periphery surface of dispersion chamber bottom member 72 and the inner periphery surface of inside cylindrical member 64. Also, the glass 78 is disposed in insertion tube 72 a placed at the center of dispersion chamber bottom member 72 and ceramic adhesive is filled into insertion tube 72 a. Bus bars 80 extending from current collector 82 penetrate this glass 78 and the ceramic adhesive. In this state, the above-described heating step is carried out on the assembly, hardening the ceramic adhesive.

Next, as shown in FIG. 9, the assembly is vertically inverted and the current collector 82 is attached to the tip portions of the individual fuel cells 16 affixed so as to project out from collection chamber lower member 18 b. In addition, collection chamber upper member 18 a is disposed on collection chamber lower member 18 b, and ceramic adhesive is filled into the gap between collection chamber upper member 18 a and collection chamber lower member 18 b. Also, the large diameter seal 19 a and the small diameter seal 19 b are disposed on the ceramic adhesive. In this state, the above-described heating step is implemented on the assembly to form ceramic adhesive layers 120 a and 120 b (see FIG. 4).

Next, inside cylindrical container 68 and outside cylindrical container 70 are attached to the assembly by welding or ceramic adhesive. Thereafter, ceramic adhesive is filled into the gap between outside cylindrical member 66 and inside cylindrical container 68 and hardened by the above-described heating step. After this heating step, the second heating step is carried out to a still higher temperature (e.g., approximately 650° C.), hardening each ceramic adhesive layer to a state capable of withstanding the temperature rise at the startup step.

The assembly shown in FIG. 2 is manufactured by the aforementioned steps, and finally a reduction step is performed. In this reduction step, a high temperature reduction gas (fuel gas; i.e., hydrogen gas) is supplied from fuel gas supply pipe 90 inside a high temperature (e.g., approximately 650° C.) oven, and reduction gas passes over the fuel electrode side of each fuel cell 16. By this means, fuel electrodes which had oxidized are reduced in a high temperature reduction gas atmosphere so that, for example, the nickel oxide contained in the fuel electrode can be reduced to nickel.

Note that the reduction step may be executed after the assembly is returned to a low temperature following execution of the above-described second heating step, or may be continuously executed following the second heating step, or both steps may be simultaneously executed.

Next, of the steps used to manufacture the solid oxide fuel cell device 1 according to an embodiment of the present invention, we shall explain in detail the method for affixing current collector 82 to a cell array of fuel cells 16.

First, referring to FIGS. 10 through 12, we explain a first embodiment.

FIG. 10 is an explanatory diagram of a method for affixing a current collector; FIG. 11 is a flow chart of an affixing method; and FIG. 12 is an explanatory diagram showing the state in which a current collector is affixed to an individual fuel cell.

Each fuel cell 16 has a cylindrical porous support body 97; fuel electrode layer 98, reaction suppression layer 99, solid electrolyte layer 100, air electrode layer 101, electrode layers 103 a and 103 b, and lead film layers 104 a and 104 b are formed on the outer periphery surface of the support body (see FIG. 6).

First, as shown in FIG. 10(a), an electrically conductive adhesive 151 is applied to the exposed surfaces of electrode layers 103 a, 103 b on both end portions of individual fuel cells 16 (FIG. 11, step S1). This adhesive application step is performed before a plurality of individual fuel cells 16 are modularized into a cell array, i.e., to each fuel cell 16 in a standalone state.

Adhesive 151 in the present embodiment is a mixture of solid powder 151 b into a binder component 151 a, and is in a paste state prior to hardening. Any of α-terpineol, nonionic surfactant, or a mixture of polyvinyl butyral and polyacetal, for example, may be used as a binder component. The solid powder may be a granular electrically conductive material which sinters at a temperature at or below the operating temperature of solid oxide fuel cell device 1 (e.g., approximately 600° C. or above), for example nickel powder. The average grain size of the powder is set to be approximately the same or less than the pore diameter of the electrode layer, which is a porous body. The powder in the present embodiment has a grain size on the order of μms to several tens of μms. Therefore in the adhesive application step, a portion of binder component 151 a and solid powder 151 b of the adhesive 151 penetrates into the pores of the electrode layer, which is a porous body, or is disposed to block the openings in the electrode layer pores.

Next, as shown in FIG. 10(b), adhesive 151 is heated and binder component 151 a dried (FIG. 11, step S2). This drying step (first hardening step) can dry the binder component 151 a in the same way, for example, as the above-described heating step, by disposing the individual fuel cells 16 in an atmosphere of approximately 80° C. inside a drying oven. The drying temperature in the drying step can dry binder component 151 a, but is set to a temperature at or below needed to sinter solid powder 151 b. Note that the above-described ceramic adhesive heating step may also double as this drying step.

In the drying step, the drying of binder component 151 a results in the formation of an electrode protective layer 152, comprised primarily of solid powder 151 b, in entire pores of the electrode layer or in pores close to the surface thereof (the electrode protective layer forming step).

The electrode protective layer 152 of the present embodiment primarily comprises fine nickel powder, and is harder than the electrode layer. By covering the electrode layer, the electrode protective layer 152 can protect the electrode layer from outside forces.

Next, by affixing individual fuel cells 16 on which an electrode protective layer 152 is formed, with the fuel cells 16 positioned to first affixing member 63 and collector chamber lower member 18 b (see FIG. 8), the cell array composed of a plurality of individual fuel cells 16 is modularized (FIG. 11, step S3).

Next, as shown in FIG. 10(c), a current collector attaching step is performed to attach current collectors 82 to both respective end portions of modularized individual fuel cells 16 (FIG. 11, step S4). Specifically, as shown by the imaginary line in FIG. 10(c), each of the current collector plates 83 a-83 e of current collector 82 is positioned with respect to the cell array. That is, each current collector plate is disposed so that the center of the attaching holes 84 on current collector 82 is positioned on approximately the axial center of the corresponding individual fuel cell 16. As shown by the solid line in FIG. 10(c), current collector 82 is pressed into the cell array. By this means, individual fuel cells 16 are inserted into the corresponding attaching holes 84. At this point, the plurality of elastic pieces 84 a on attaching holes 84 elastically bend along the outer periphery surface of individual fuel cells 16, contacting the outer periphery surface thereof. When each of the current collector plates is pressed into a predetermined position, elastic pieces 84 a elastically engage with electrode protective layer 152. Elastic pieces 84 a and electrode protective layer 152 are in this way electrically connected.

When current collector 82 is attached to a cell array, current collector 82 moves to a predetermined position as the bending elastic pieces 84 a contact electrode protective layer 152 formed on the outer periphery surfaces of fuel cells 16. At this point, the electrode layers of individual fuel cells 16 are covered by an electrode protective layer 152 and therefore protected from damage caused by contact with elastic pieces 84 a. Therefore in the present embodiment a current collector 82 comprising elastic pieces 84 a having a large elastic force can be used.

Next, as shown in FIG. 10(d), an adhesion step (second hardening step) is executed to adhere elastic pieces 84 a and electrode protective layer 152 (FIG. 11, step S5). Specifically, a step is executed whereby electrode protective layer 152 is heated to a temperature at or below the melting point of solid powder 151 b, and solid powder 151 b is sintered. Sintering causes electrode protective layer 152 to shrink in volume and densify. This sintering step may be executed for only the purpose of adhering current collector 82 and individual fuel cells 16, but the above-described ceramic adhesive second heating step or the reduction step can also double as sintering step. The manufacturing process can be shortened if the second heating step or the reduction step are constituted to double as sintering step.

In this embodiment, nickel powder is used as solid powder 151 b. Therefore sintering of solid powder 151 b gradually starts from about 250° C., and is completed during the rise to approximately 550° C. As a result, in the second heating step or reduction step doubling as sintering step, the sintering step can, for example, be completed in the process of the gradual temperature rise up to approximately 650° C.

On the other hand, in the present embodiment current collector 82 is formed of nickel plate, and when the temperature of current collector 82 rises, there is a risk that the coefficient of elasticity of the plate material will drop, or that recrystallization will occur, causing elastic force to drop. When elastic force drops due to a drop in the coefficient of elasticity or a drop in elastic force, the pressing force of elastic pieces 84 a on electrode protective layer 152 drops, with the risk that contact will be lost between elastic pieces 84 a and electrode protective layer 152. The temperature for nickel recrystallization is approximately 530° C. to approximately 660° C.

However, in the present embodiment the material for the current collector 82 and the solid powder 151 b contained in adhesive 151 is selected so that the sintering of electrode protective layer 152 is completed or at least partially completed while the nickel plate material of the current collector 82 has elastic force. Specifically, in the present embodiment the grain size, etc. of solid powder 151 b is set so that solid powder 151 b sinters before the recrystallization of current collector 82. Hence in the sintering step, elastic pieces 84 a can be adhered to electrode protective layer 152.

Moreover, in the present embodiment electrode protective layer 152 is formed on the surface of the electrode layer before the current collector attaching step, therefore when attaching a current collector, scratching and damage (peeling) of the electrode layer by elastic pieces 84 a can be prevented. For this reason elastic pieces 84 a with a comparatively large elastic force can be used. That is, current collector 82 can be formed from a plate material with a comparatively large sheet thickness. If elastic pieces 84 a have a high elastic force, a comparatively large elastic force can be maintained by elastic pieces 84 a even if individual fuel cells 16 and current collector 82 are exposed to high temperatures during operation of solid oxide fuel cell device 1. Thus even if there is no adhesive force in electrode protective layer 152 from the execution of an adhesion step, elastic pieces 84 a can engage the electrode layer with the elastic force thereof and maintain an electrical connection.

If solid powder 151 b is heated in the sintering step, at least the surface part of solid powder 151 b will have fluidity, and a partial molten state will be attained. At this point, electrode protective layer 152 is pressed by the elastic force of elastic pieces 84 a, therefore the tip portion of elastic pieces 84 a partially sinks into or is buried in electrode protective layer 152. At the point of completion of sintering, solid powder 151 b loses its fluidity and enters a solid state. The change from a fluid state to a solid state in electrode protective layer 152 activates the adhesion function. Thus when electrode protective layer 152 is sintered, elastic pieces 84 a are strongly adhered to the sintered electrode protective layer 152, as shown in FIG. 12. Thus physical displacement of elastic pieces 84 a relative to the electrode layer can be prevented when stress or an external load such as heat is applied to elastic pieces 84 a during operation. Hence electrical conductivity between current collector 82 and the cell array is secured through the electrically conductive electrode protective layer 152.

Thus in the sintering step the contact surface area between elastic pieces 84 a and the adhesive is increased by the partial sinking or covering up of elastic pieces 84 a in the adhesive (electrode protective layer 152), strengthening the degree of bonding between the two and enabling the electrical resistance between elastic pieces 84 a and the electrode layer to be reduced.

Also, in the present embodiment the manufacturing process is simplified by forming electrode layers 103 a, 103 b of the same porous material as fuel electrode layer 98 and air electrode layer 101. For this reason the electrode layer has a porous structure, so there is a risk that electrical conductivity may not be very good, or that contact resistance will be high. In this embodiment, however, electrode protective layer 152 is formed not only on the surface of the electrode layer but also inside the pores of a surface layer of the electrode layer, enabling an improvement in the electrical conductivity of the electrode layer and reduction in electrical resistance between electrode protective layer 152 and the electrode layer to constitute a more efficient fuel cell.

In addition, after the solid powder 151 b penetrating the pores of the electrode layer of porous structure reaches a partially melted state, then solidified and densified as a result of the sintering of electrode protective layer 152, the electrical conductive pathway inside the porous structure is substantially expanded. This enables a densified interconnector structure with high electrical conductivity to be formed.

Moreover, in the process of densification during the sintering step, electrode protective layer 152 is pressed by elastic pieces 84 a, permitting the density of electrode protective layer 152 to be increased at the locations where elastic pieces 84 a press upon the electrode layer. This enables a still further increase in electrical conductivity in the electrically conductive pathway near elastic pieces 84 a.

In addition, in the present embodiment the adhesion step doubles as a densification step, allowing the manufacturing process to be simplified.

If the adhesion application step is executed after a plurality of fuel cells 16 are modularized into a cell array, the adhesion application step becomes extremely cumbersome. However, in the present embodiment the adhesive application step and the binder drying step can be executed on individual fuel cells 16 in a freestanding state before modularization. In the present embodiment, this enables the manufacturing process to be simplified without burdensome work.

Note that in the present embodiment electrode protective layer 152 doubles as an adhesive, but without such limitation, an adhesive separate from electrode protective layer 152 could additionally be used, adhering elastic pieces 84 a still more strongly to electrode protective layer 152. The use of a different adhesive is valid if the adhesive function from electrode protective layer 152 is insufficient or electrode protective layer 152 has no adhesive function.

Next, referring to FIG. 13, we explain a second embodiment of the method for affixing a current collector.

In the above-described first embodiment, the adhesive application step and binder drying step are executed on each fuel cell 16 before the plurality of individual fuel cells 16 are modularized into a cell array, but the adhesive application step and binder drying step can also be executed on the cell array after the modularization step.

That is, in the second embodiment, as shown in FIG. 13, the following steps are executed in this order: a modularization step (step S11), an adhesive application step (step S12), a binder drying step (step S13), a current collector attaching step (step S14), and an adhesion step (step S15).

This constitution enables the binder drying step to be executed at the same time as the ceramic adhesive heating step, thus enabling a shortening of the manufacturing process and a reduction in energy use.

Next, referring to FIGS. 14 and 15, we explain a third embodiment of the method for affixing a current collector.

In the third embodiment, a plurality of fuel cells 16 are first modularized in a cell array, as shown in FIG. 8 (FIG. 15, step S21).

Next, as shown in FIG. 14(a), electrically conductive adhesive 151 is applied to the surface of electrode layers 103 a, 103 b (FIG. 15, step S22). In this adhesive application step, adhesive 151 in a paste state is applied thickly onto the surface of the electrode layers. Adhesive 151 comprises a binder component 151 a and an electrically conductive solid powder 151 b, and is the same as that in the embodiment shown in FIG. 10.

However, it is preferable for the viscosity of adhesive 151 to be at a level permitting it to pool on the electrode layer after application, so that it can be thickly applied. Therefore in the third embodiment, an electrically conductive adhesive different from that of the FIG. 10 embodiment may be used as the adhesive 151.

Next, as shown in FIG. 14(b), each current collector plate 83 a-83 e of current collector 82 is positioned relative to the cell array (see the imaginary line in FIG. 14(b)), and each current collector plate is pushed into the cell array (FIG. 15, step S23). By this means, individual fuel cells 16 are inserted into corresponding attaching holes 84. When each current collector plate has been pushed into a predetermined position, the elastic pieces 84 a on attaching holes 84 are positioned on the side of electrode layers 103 a, 103 b of fuel cell 16 (see the solid line in FIG. 14(b)).

Individual fuel cells 16 are formed of a ceramic material, and are difficult to form with high dimensional accuracy. For this reason, variability in length, diameter, bend, etc. occurs between the plurality of individual fuel cells 16. There is therefore a risk that attaching holes 84 will be offset from their corresponding individual fuel cells 16 even if current collector 82 is positioned relative to the cell array. Hence in the current collector attaching step (step S23) there is a risk that some of the elastic pieces 84 a will not contact the electrode layer surface when current collector 82 is temporarily attached to the cell array. For example, the elastic piece 84 a on the right side of FIG. 14(b) is contacting the electrode layer surface, but the electrode 84 a on the left side is not contacting the electrode layer surface.

Therefore in the adhesive application step (step S22) the fuel cell 16 dimensional error is taken into account and adhesive 151 is applied thickly on the electrode layer. By so doing, in the current collector attaching step, an elastic piece 84 a not contacting the surface of an electrode layer can be buried in adhesive 151, or at least can be placed in a state of contact with adhesive 151.

Next, as shown in FIG. 14(c), adhesive 151 is heated and binder component 151 a dried (FIG. 15, step S24). This drying step is the same as the drying step explained in relation to FIG. 10(b).

By this drying step, the elastic piece 84 a on the right side of FIG. 14(c) is affixed to the electrode layer, a portion of which is covered by electrode protective layer 152 comprising solid powder 151 b, in a state of contact with the surface of the electrode layer. At the same time, the elastic piece 84 a on the left side of FIG. 14(c) does not contact the surface of the electrode layer, but is affixed to the electrode layer via electrode protective layer 152.

Next, as shown in FIG. 14(d), an adhesion step is executed to adhere elastic pieces 84 a and electrode protective layer 152 (FIG. 15, step S25). This adhesion step is the same as the drying step explained in relation to FIG. 10(d).

By this adhesion step, elastic pieces 84 a are strongly adhered to the electrode layer. The elastic piece on the right side of FIG. 14(d) is adhered to the electrode layer by electrode protective layer 152 in a state of contact with the surface of the electrode layer, thereby securing direct electrical conductivity with the electrode layer. At the same time, the elastic piece 84 a on the left side of FIG. 14(d) is not contacting the electrode layer surface, but because it is adhered to the electrode layer through electrode protective layer 152, electrical conductivity with the electrode layer is secured through electrode protective layer 152, which is electrically conductive.

Thus in the third embodiment, even when the dimensional error in individual fuel cells 16 is comparatively large, and there is no contact with the electrode layer by some elastic pieces 84 a after execution of the current collector attaching step, an electrical connection can be reliably made between all of the elastic pieces 84 a and the electrode layer.

Also, even if the elastic force of the elastic pieces 84 a of current collector 82 drops due to a rise in the temperature of current collector 82 up to the operating temperature when solid oxide fuel cell device 1 is operating, displacement of elastic pieces 84 a relative to the electrode layer is prevented by adhesion, so that electrical conductivity between elastic pieces 84 a and the electrode layer is secured by electrode protective layer 152.

Next, referring to FIGS. 16 and 17, we explain a fourth embodiment of the method for affixing a current collector.

In the fourth embodiment, a plurality of fuel cell 16 are first modularized in a cell array, as shown in FIG. 8 (FIG. 17, step S3).

Next, as shown in FIG. 16(a), each current collector plate 83 a-83 e of current collector 82 is positioned relative to the cell array (see the imaginary line in FIG. 16(a)), and each current collector plate is pushed into the cell array (FIG. 17, step S32). By this means, individual fuel cells 16 are inserted into the corresponding attaching holes 84. When each current collector plate has been pushed in to a predetermined position, the elastic pieces 84 a on attaching holes 84 elastically engage electrode layers 103 a, 103 b of fuel cell 16 (see the solid line in FIG. 16(a)).

Next, as shown in FIG. 16(b), an adhesive 153 is applied between each of the elastic pieces 84 a and electrode layers 103 a, 103 b (FIG. 17, step S33); adhesive 153 is hardened, and elastic pieces 84 a and the electrode layer are adhered (FIG. 17, step S34).

Note that the electrically conductive adhesive used in the first embodiment may be used for adhesive 153, or another electrically conductive adhesive may be used. In this case, after execution of the current collector attaching step (step S32), electrical conductivity can be secured through adhesive 153 even if some of the elastic pieces 84 a do not contact the electrode layer.

Also, a non-electrically conductive adhesive may be used as adhesive 153. In such a case, after execution of the current collector attaching step, electrical conductivity can be secured between those elastic pieces 84 a and the electrode layer, at least with respect to elastic pieces 84 a contacting the electrode layer.

Also, in the present embodiment even if the elastic force of elastic pieces 84 a of current collector 82 drops due to a rise in the temperature of current collector 82 up to the operating temperature when solid oxide fuel cell device 1 is operating, electrical conductivity between elastic pieces 84 a and the electrode layer is secured by adhesive 153.

As described above, because the dimensional error in individual fuel cells 16 is relatively large, there is a risk in the current collector attaching step (step S32) that individual fuel cells 16 will be offset relative to corresponding attaching holes 84, even if current collector plates are positioned relative to the cell array. Therefore there is a need to press the current collector plates onto the cell array with a comparatively large pressing force, but if the current collector plates are pressed excessively there is a risk that exposed electrode layers 103 a, 103 b will be damaged (e.g., peeling the electrode layer, etc.) by elastic pieces 84 a. To prevent such damage, one conceivable method is to form current collector 82 of an even thinner plate material so as to reduce the elastic force of elastic pieces 84 a. However if the elastic force is reduced, then the elastic force of elastic pieces 84 a will be further diminished when current collector 82 is exposed to high temperatures during operation of solid oxide fuel cell device 1, leading to the risk that contact between elastic pieces 84 a and the electrode layer will lost.

Therefore in the fourth embodiment, displacement of elastic pieces 84 a from the electrode layer is prevented by affixing elastic pieces 84 a and the electrode layer with adhesive 153, so that non-contact with the electrode layer can be prevented at high temperatures. Hence the use of a current collector 82 with elastic pieces 84 a having a low elastic force setting is enabled, and by forming current collector 82 of a thin sheet material, manufacturing cost and reduced device weight can be achieved. 

What is claimed is:
 1. A solid oxide fuel cell device comprising a cell array including a plurality of fuel cells housed in a fuel cell module, and a current collector electrically connected to electrodes formed on end portions of the plurality of fuel cells, wherein the current collector comprises a metal plate having (i) a plurality of attaching holes formed through the metal plate, wherein the end portions of the plurality of individual fuel cells are inserted, respectively, in the plurality of attaching holes, and (ii) a plurality of sets of elastic pieces provided, respectively, at the plurality of attaching holes, wherein a respective set of elastic pieces is in electrical contact with a corresponding fuel cell inserted in an attaching hole to which the respective set of elastic pieces is attached, and the plurality of sets of elastic pieces provide an electrically connection between the current collector and the cell array, and the respective set of elastic pieces are adhered to the corresponding fuel cell by means of an adhesive so that the respective set of elastic pieces is secured on the electrode of the corresponding fuel cell, and further wherein the solid oxide fuel cell device comprises an electrically conductive electrode protective layer harder than the electrodes and provided between the respective set of elastic pieces and the electrode of the corresponding fuel cell to prevent direct contact between the plurality of sets of elastic pieces and the electrodes of the plurality of fuel cells to prevent damage to the electrode that could occur when the plurality of fuel cells are inserted, respectively, into the plurality of attaching holes of the current collector, wherein the electrode protective layers are sintered to function as the adhesive to secure the plurality of sets of elastic pieces to the electrodes of the plurality of fuel cells.
 2. The solid oxide fuel cell device of claim 1, wherein the respective set of elastic pieces comprise tab portions bent over the electrode of the corresponding fuel cell in electrical contact with the electrode of the corresponding fuel cell, and the adhesive is applied to cover at least the tab portions of the respective set of elastic pieces.
 3. The solid oxide fuel cell device of claim 1, wherein the adhesive is electrically conductive and is disposed between the respective set of elastic pieces and the electrode of the corresponding fuel cell, and the adhesive is hardened to include, inside thereof, at least the tab portions of the respective set of elastic pieces. 